1. Field of the Invention
The present invention is generally directed to the treatment of dysphagia, and is more specifically directed to an electrical stimulation device and method for applying a series of electrical pulses to one or more channels of electrodes in accordance with a procedure for treating dysphagia.
2. Description of Related Art
Swallowing is a complicated action whereby food is moved from the mouth through the pharynx and esophagus to the stomach. The swallowing act is usually divided into several stages that require the integrated action of the respiratory center and motor functions of multiple cranial and cervical nerves, as well as the coordination of the autonomic system.
The first stage (commonly referred to as the oral stage) involves mastication, bolus formation and bolus transfer. The food, which has been brought to the mouth, is chewed and combined with saliva to form a bolus that is moved to the back of the oral cavity and prepared for swallowing. The performance of the oral phase requires proper lip closure, cheek tensing, multidimensional tongue movement and chewing.
The second stage (commonly referred to as the oropharyngeal stage) involves the coordinated contractions of several muscles of the tongue, pharynx and larynx, whereby the bolus is moved to the back of the throat and into the esophagus. The tongue propels the bolus to the posterior mouth into the pharynx. The bolus passes through the pharynx, which involves relaxation and constriction of the walls of the pharynx, backward bending of the epiglottis, and an upward and forward movement of the larynx and trachea. The bolus is prevented from entering the nasal cavity by elevation of the soft palate and from entering the larynx by closure of the glottis and backward inclination of the epiglottis. During the oropharyngeal stage, respiratory movements are inhibited by reflex.
The third stage (commonly referred to as the esophageal stage) involves the movement of the bolus down the esophagus and into the stomach. This movement is accomplished by momentum from the prior stage, peristaltic contractions and gravity.
Dysphagia is generally defined as difficulty in swallowing. For example, dysphagia may occur when one cannot create a good lip seal/closure (which results in the leaking of the mouth contents) or ineffective tongue plunger action. Also, poor cheek tensing may result in the pocketing of food between the teeth and cheek. The patient may sometimes be unable to complete chewing due to muscle fatigue of the tongue and the muscles involved in mastication.
Classic neurologically-based dysphagia is described as a dystonia or incoordination of the oropharyngeal stage sequencing of multiple muscles controlled by the central pattern generator located in the brainstem. This level of dysphagia may manifest itself as the bolus being lodged in the throat after swallowing. The patient may even regurgitate the food or most dangerously aspirate into the airway.
Dysphagia has a variety of causes. These include obstructive/mechanical, damage to the central neuron pools (pattern generators) for swallowing following traumatic injury, or neurologic disease (as in stroke), nerve compression, neuromuscular junction atrophy or damage, and muscular atrophy and spasticity. Dysphagia may also be a sign of underlying disease of the esophagus, which may be due to strictures, gastroesophogeal reflux disease, peptic ulcers, cancer, thyroid disease, stroke, Parkinson's disease, ALS, myasthenia gravis, muscular dystrophy, muscular atrophy, torticollis, or a number of other diseases. Dysphagia may also be medication-induced.
In the past, patients suffering from dysphagia have been subjected to dietary changes or thermal and mechanical stimulation treatments to regain adequate swallowing reflexes. Thermal stimulation involves immersing a mirror or probe in ice or another cold substance and stimulating the tonsillar fossa with the cold mirror or probe. Upon such stimulation, the patient is directed to close his mouth and attempt to swallow. While dietary changes and exercise rehabilitation using thermal stimulation may be effective for treating dysphagia, some patients may require weeks or months of therapy. It is also difficult to distinguish patients who require such treatments from patients who recover spontaneously.
Electrical stimulation of various body parts has also been used in order to treat dysphagia. For example, Kaada and other researchers have reported that low-frequency transcutaneous nerve stimulation on the hands resulted in relief from dysphagia. See Kaada, Successful treatment of esophageal dysmotility and Raynaud's phenomenon in systemic sclerosis and achalasia by transcutaneous nerve stimulation: Increase in plasma VIP concentration, Scand. J. Gastroenterol. 1987 Nov. 22(9):1137-46; Kaada, Systemic sclerosis: successful treatment of ulcerations, pain, Raynaud's phenomenon, calcinosis, and dysphagia by transcutaneous nerve stimulation: A case report, Acupunct. Electrother. Res. 1984 9(1):31-44; Guelrud et al., Transcutaneous electrical nerve stimulation decreases lower esophageal sphincter pressure in patients with achalasia, Dig. Dis. Sci. 1991 Aug. 36(8):1029-33; Chang et al., Effect of transcutaneous nerve stimulation on esophageal function in normal subjects—evidence for a somatovisceral reflex, Am. J. Chin. Med. 1996 24(2):185-92. However, other researchers have found no beneficial effects associated with esophageal motility upon applying electrical simulation to the hands. See Mearin et al., Effect of transcutaneous nerve stimulation on esophageal motility in patients with achalasia and scleroderma, Scand. J. Gastroenterol. 1990 Oct. 25(10):1018-23.
More recently, electrical stimulation has been applied to the oral cavity for the treatment of dysphagia. See Park et al., A pilot exploratory study of oral electrical stimulation on swallow function following stroke: an innovative technique, Dysphagia. 1997 Summer 12(3):161-6. Other researchers have reported improved swallowing with the use of transcutaneous electrical stimulation applied to the anterior portion of the neck (i.e., the region bounded on the upper side by the mandible and on the lower side by the clavicles and the manubrium of the sternum). See Freed et al., U.S. Patent Application No. 2004/0220645 entitled “Treatment of oropharyngeal disorders by application of neuromuscular electrical stimulation”; Freed et al., U.S. Pat. No. 5,725,564; Freed et al., U.S. Pat. No. 5,891,185; Freed et al., U.S. Pat. No. 5,987,359; and Freed et al., U.S. Pat. No. 6,198,970. The Freed method may pose a safety hazard to the patient if the electrodes and stimulation are inadvertently placed over the carotid sinus (which may alter blood pressure and/or cardiac contractility). In addition, a risk occurs if the electrodes and stimulation are applied anteriorly over the laryngeal or pharyngeal muscles (which may cause a blockage of the patient's airway and cause difficulty in breathing due to electrical activation of the muscles causing a strong contraction). Further, when the electrodes are placed on the anterior neck and the chin is tucked for swallowing, the electrodes may contact each other shorting out and causing uncomfortable or dangerous surges in current. Loose skin, adipose tissue and facial hair further limit the placement and adhesion of electrodes to the target treatment area. Thus, there is a need in the art for an improved or alternative method for treating dysphagia.